X-ray systems typically serve to pass X-radiation through bodies in various directions and with various orientations. An X-ray source generates an X-ray beam, which passes through a body to be examined and is then received by an X-ray receiver. Various orientations in three dimensions are achieved by providing that the X-ray source can be positioned and oriented variably in terms of three dimensions. So that the X-ray beam can be picked up, the X-ray receiver is positioned in a predetermined position relative to the X-ray source.
An image section, image geometry, and a quality of an X-ray image can be affected by the relative position of the X-ray source and the X-ray receiver. Incorrect or imprecise positioning can cause problems that may necessitate retaking unsuccessful radiographs, which involves considerable effort on the part of medical personnel as well as additional radiation exposure to the body of a patient, for instance, who is to be examined.
Substantially precise relative positioning of the X-ray source and X-ray receiver can be attained using a light collimator, for instance. The light collimator projects an optical image, such as crosshairs, from the X-ray source and this image can be aligned with the X-ray receiver by a machine operator or user. The manual alignment can involve considerable operator effort, and may only conditionally enable exact setting of the direction, spacing and orientation. The spacing and orientation cannot be adequately exactly perceived by the machine operator on the basis of an optical projection. Light collimators are therefore primarily employed for aligning the X-ray source with the body region to be examined.
For substantially exact detection of the relative positioning, angle encoders and travel pickups are usually utilized in the mechanism of an X-ray system. For example, the X-ray source can be mounted horizontally displaceable, vertically adjustable, and rotatable about both a vertical and a horizontal axis on a ceiling-mounted tripod. Such a tripod can enable a completely flexible three-dimensional mobility of the X-ray source. To detect the three-dimensional position and orientation at a given time, travel pickups are mounted on the X-ray system mechanism for the horizontal displacement and vertical adjustment, and angle encoders are mounted on the axes for the horizontal and vertical rotation.
Via the travel pickups, the three-dimensional orientation and position of the X-ray source are accordingly fundamentally detectable, as are those of the X-ray receiver. However, a plurality of pickups is needed, which increases a vulnerability or susceptibility to error because of compounding measurement tolerances. Moreover, the measurement is subject to errors due to a heavy weight, for instance of an X-ray source, an elasticity, for instance of a ceiling-mounted tripod, and because typically components deform elastically under load. The component deformation, however, cannot be detected by the travel pickups and angle encoders.
From German Patent Disclosure DE 196 11 705, it is known, instead of indirect detection by travel pickups and angle encoders, to provide for direct detection of the orientation and position, that is, a detection of the actual state. As such, measuring mechanisms that enable detecting the three-dimensional position, or position in space, are mounted on the X-ray source and on the X-ray receiver. The relative three-dimensional position can be ascertained or determined using t space coordinates. The indirect nature of determining the relative position by first ascertaining the current three-dimensional position can increase the vulnerability to error. Moreover, the measuring mechanisms for ascertaining a given position in space are complicated because, to ascertain the respective orientation, the space coordinates of all three points for a device must be ascertained.